Former UDC president Robert L. Green, taking the witness stand on his own behalf, denied yesterday that he asked a top aide to Mayor Marion Barry for $1,400 in cash to reimburse a private university fund for the purchase of a stereo for the president's official home.

"I absolutely did not ask him for cash," said Green, who has been on trial for the past week on charges of fraud, theft and lying to a federal grand jury investigating expenditures from special accounts controlled by Barry's office.

During more than an hour of questioning by his attorney, R. Kenneth Mundy, Green stood by two portions of his grand jury testimony that the indictment of Green charges are false.

Green said the aide, Dwight S. Cropp, told him the money provided for the stereo and later for the purchase of a projection television was not city money but came from a special account in the mayor's office financed by private donations solicited by D.C. businessman Jeffrey Cohen.

"That, Mr. Mundy, is a true statement, not a false statement," Green said.

Cropp testified that he never told Green there was any fund controlled by Cohen.

Cropp, currently Barry's director of intergovernmental relations and formerly the official who controlled the mayor's discretionary funds, testified last week that he told Green the money for both the television and the stereo was from city funds. Cropp said Green promised to reimburse the mayor's funds through interagency fund transfers from the University of the District of Columbia.

Green, who is scheduled to continue his testimony today, has not been questioned about other portions of his allegedly false statements to the grand jury, but the testimony yesterday of his wife, Lettie C. Green, contradicted other statements Green made to the grand jury.

Lettie Green said that she and her husband used the television and stereo system frequently after they moved from the university president's house at 3520 Rittenhouse St. NW in November 1985 to a private condominium at 4301 Massachusetts Ave. NW and that the equipment was to be moved in May 1987 to their new home in Ohio.

Robert Green told the grand jury in August 1987 that he had not decided whether the television and stereo would go to their Ohio home, and Mundy has suggested that the Greens did not use the items at their private District residence.

The $1,399 Sansui stereo system and the $1,994.90 Hitachi projection television were seized May 2 by the FBI from a local moving company.

Lettie Green told the jury that she believed the stereo belonged to her and her husband because she had received a canceled check on their personal banking account made out to the UDC Fund and marked as reimbursement for the stereo. She testified that she did not discuss the purchase of the television or stereo with her husband and never talked to him about who owned them.

Cropp, who in late 1983 and early 1984 served as an assistant to both Barry and Green, is the key prosecution witness against Green and much of Mundy's questioning of witnesses has appeared to raise questions about Cropp's possible conflicting loyalties.

During Green's testimony, which began with a 20-minute recitation of his job history and work in the civil rights movement, Green said that Barry had asked him to hire Cropp at the university and that he had done so despite a concern by Ronald Brown, head of the university's trustees, that such an appointment might infringe on the school's independence.

Describing the transactions involving the stereo purchase, Green testified that Cropp had volunteered to provide the money to reimburse the UDC Fund for the stereo. Earlier testimony in the trial showed that the fund refused to purchase the stereo outright, but had provided Green a loan.

"Let me handle it. That was a favorite statement of Mr. Cropp's," Green said, describing his conversation with Cropp.

Green said the matter came up after arrangements for the purchase of the stereo became widely known on the campus at the time negotiations were beginning for faculty raises.

"I did not want the stereo to become an issue at the same time we were considering faculty salaries," Green said.